Low-pressure gradient

Where binary, ternary or quaternary gradient elution (p. 91) is required, a microprocessor controlled low-pressure gradient former is the most suitable (Figure 4.31(c)). The solvents from separate reservoirs are fed to a mixing chamber via a multiport valve, the operation of which is preprogrammed via the microprocessor, and the mixed solvent is then pumped to the column. For the best reproducibility of solvent gradients small volume pumps (< 100 gl) are essential. 

Hardware contributions to gradient performance High-pressure or low-pressure gradient formation Mixing devices Gradient precision Developing a gradient separation The three basic situations... 

Figure 4.26(c). A low-pressure gradient former with three solvents... 

Reticulation is an after-treatment that removes residual cell membranes to produce a foam with a skeletal rib structure. Reticulated foams are very effective filters for the removal of dust and fibers from air and other gases. They allow high flow rates and low pressure gradients (i.e., minimal energy consumption). Methods of reticulation include chemical hydrolysis and the use of an explosion flame front to melt the membranes.f ... 

Figure 4.2 Low-pressure gradient system (top) and high-pressure system (bottom).

Flush the pump with open drain valve at high flow rate. Degas the mobile phase or use an on-line degasser. (This is absolutely necessary with low-pressure gradient systems.) Clogged inlet filter of the pump ... 

SLM usually is the progressive loss of the liquid embedded in the membrane into the surrounding phases due to liquid vaporization, dissolution into the adjacent liquid phases and/or shifting from the porous structure of the supported membrane under low-pressure gradients [2]. The use of ionic liquids as liquid phase could overcome these inconveniences due to their unique properties [3-5]. Ionic... 

V(. with modern instrumentation is better than 1 %, often around 0.5 %. Users seem to slightly prefer low-pressure gradient mixers over high pressure gradient mixers. Degassing units are often built-in. Many instruments are capable of working with miniaturized columns. 

---